This invention relates to shaft couplings that achieve flexibility and shock absorbing functions by use of coil springs as their resilient torque-transmitting elements.
Various types of shaft couplings that transmit torque by means of coil springs are marketed because of their relatively large shaft-misalignment accommodating and shock-absorbing capacities.
FIG. 1 shows an example of such conventional coil-spring shaft couplings. This shaft coupling is composed of two mating hubs 1 each of which, in turn, has a plurality of holes 2 in which coil springs are fitted. A coil spring 3 is interposed between the two hubs 1 with one end thereof fitted in one of the corresponding spring holes 2 and the other end in the other. Torque is transmitted from one of the hubs 1 to the other via the coil spring 3. Accommodation of misalignment and shock absorption are achieved by the lateral deformation of the coil spring with respect to the axis thereof.
Although simple in construction, the shaft coupling in FIG. 1 has the following problems: With the coil spring 3 loosely fitted in the spring holes 2, there is a backlash between the coil springs and the spring holes 2 that lowers the accuracy of the rotational angle. Besides, the spring holes 2 are enlarged during use by impact and abrasion caused by the coil spring 3, with the results that the accuracy of the rotational angle becomes still lower and that the coil spring 3 fractures by fatigue failure after a relatively short period of use.
Since the coil spring is not rigidly but only loosely or movably fitted in the spring holes, the shaft coupling of the type just described is unsuitable for the transmission of large torques.
This invention concerns the improvement of the shaft coupling shown in FIG. 1 and that has the advantage of simple construction.